The cracking resistance is an important indicator concerned by the industry. In this study, the cracking resistances (impact toughness, fracture toughness and fatigue crack growth resistance) of different ageing treated 18Ni maraging steels were investigated. Meanwhile, the differences in microstructures and fractographies were compared. Finally, the key factors affecting the cracking resistances were discussed and confirmed. It is found that, with the increment in ageing temperature, the size and spacing of precipitated phases would augment, as well as, the impact and fracture toughness, and fatigue crack growth resistance would improve. The fracture morphologies of impact and fracture toughness specimens display that, with the improvement of toughness, the size of dimple would gradually upgrade, and the characteristic of cleavage fracture would gradually disappear. The key factor influencing the cracking resistances of maraging steel is the interparticle spacing. Augmenting the interparticle spacing would cause the improvement of cracking resistances for maraging steel.